Overview

Hemoglobin is the substance inside red blood cells that carries oxygen to the cells of the body. Glucose (a type of sugar) molecules in the blood normally become stuck to hemoglobin molecules – this means the hemoglobin has become glycosylated (also referred to as hemoglobin A1c, or HbA1c). Hemoglobin subfractions formed by the glycation of the alpha or beta chains of hemoglobin A1 (HbA) are collectively known as glycosylated or glycated hemoglobins. Hemoglobin A1c, the best-defined of these, is formed by the reversible condensation of the carbonyl group of glucose and the amino group at the N-terminus of the beta chain of hemoglobin A, resulting in a labile aldimine or Schiff base. As the red cell circulates, some of the aldimine undergoes a slow, irreversible conversion (Amadori rearrangement) to a stable ketoamine form (HbA1c). As blood glucose levels rise, the increase in glycated hemoglobin is proportional to both the level of glucose and the lifespan of the red cell. Hemoglobin A1c measurements are used in the clinical management of diabetes to assess the long-term efficacy of diabetic control. The glycated hemoglobin result is a reflection of the mean daily blood glucose concentration and the degree of carbohydrate imbalance over the preceding two to three months.

HbA1c blood test can measure the amount of glycosylated hemoglobin in the blood. The glycosylated hemoglobin test shows what a person’s average blood glucose level was for the 2 to 3 months before the test. This can help determine how well a person’s diabetes is being controlled over time. People who have diabetes need this test regularly to see if their levels are staying within range. It can tell if you need to adjust your diabetes medicines.

HOW THE TEST IS PERFORMED

A blood sample is needed. Two methods are available:

  • Blood drawn from a vein. This is done at a lab.
  • Finger stick. This can be done in your health care provider’s office. Or you may be prescribed a kit that you can use at home.

HOW TO PREPARE FOR THE TEST

No special preparation is needed. The food you have recently eaten does not affect the A1C test, so you do not need to fast to prepare for this blood test.

HOW THE TEST WILL FEEL

With a finger stick, you may feel slight pain. With blood drawn from a vein, you may feel a slight pinch or some stinging when the needle is inserted. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

BENEFIT OF HBA1C TEST?

HbA1c is usually a reliable indicator of diabetic control except in the following circumstances:

  • Situations where the average RBC lifespan is significantly less than 120 days will usually give rise to low HbA1c results because 50% of glycation occurs in days 90-120. Common causes include:[1]
    • Increased red cell turnover: blood loss, haemolysis, haemoglobinopathies and red cell disorders, myelodysplastic disease.
    • Interference with the test (this depends on the method used: persistent fetal haemoglobin and haemoglobin variants, carbamylated haemoglobin (uraemic patients).
  • In patients who fluctuate between very high and very low levels – HbA1c readings can be misleading (the clinician should compare with extra information obtained from home capillary blood glucose tests).
  • HbA1c can be very useful in identifying patients who may be presenting an unrealistically good report of their home glucose tests.

NORMAL RESULTS

The following are the results when A1C is being used to diagnose diabetes:

  • Normal (no diabetes): Less than 5.7%
  • Pre-diabetes: 5.7% to 6.4%
  • Diabetes: 6.5% or higher

If you have diabetes, you and your provider will discuss the correct range for you. For many people, the goal is to keep the level below 7%.

The test result may be incorrect in people with anemia, kidney disease, or certain blood disorders (thalassemia). Talk to your provider if you have any of these conditions. Certain medicines can also result in a false A1C level.

The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results.

WHAT ABNORMAL RESULTS MEAN

An abnormal result means that you have had a high blood sugar level over a period of weeks to months.

If your A1C is above 6.5% and you do not already have diabetes, you may be diagnosed with diabetes.

If your level is above 7% and you have diabetes, it often means that your blood sugar is not well controlled. You and your provider should determine your target A1C. People with diseases affecting hemoglobin, such as anemia, may get misleading results with this test. Other things that can affect the results of the hemoglobin A1c include supplements such as vitamins C and E and high cholesterol levels. Kidney disease and liver diseases.

The higher your A1C, the higher the risk that you will develop problems such as:

  • Eye disease
  • Heart disease
  • Kidney disease
  • Nerve damage
  • Stroke

If your A1C stays high, talk to your provider about how to best manage your blood sugar.

RISKS

btaining a blood sample from some people may be more difficult than from others.

Other risks of having blood drawn are slight, but may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

IMPLICATIONS

Situations where HbA1c is not appropriate for diagnosis of diabetes include:

  • Children and young people.
  • Patients suspected of having type 1 diabetes.
  • Pregnancy.
  • Patients with symptoms of diabetes for less than two months.
  • Patients at high diabetes risk who are acutely ill.
  • Patients taking medication that may cause rapid glucose rise – eg, steroids, antipsychotics.
  • Patients with acute pancreatic damage, including pancreatic surgery.
  • Presence of other factors that influence HbA1c and its measurement:
    • Erythropoiesis:
      • Increased HbA1c: iron deficiency, vitamin B12 deficiency, decreased erythropoiesis.
      • Decreased HbA1c: administration of erythropoietin, iron, vitamin B12, reticulocytosis, chronic liver disease.
    • Altered haemoglobin:
      • Genetic or chemical alterations in haemoglobin: haemoglobinopathies, HbF and methaemoglobin may increase or decrease HbA1c.
    • Glycation:
      • Increased HbA1c: alcoholism, chronic kidney disease.
      • Decreased HbA1c: aspirin, vitamin C and vitamin E, certain haemoglobinopathies.
    • Erythrocyte destruction:
      • Increased HbA1c: increased erythrocyte lifespan – eg, splenectomy.
      • Decreased HbA1c: decreased erythrocyte lifespan – eg, haemoglobinopathies, splenomegaly, rheumatoid arthritis or drugs such as antiretrovirals, ribavirin and dapsone.
    • Other factors:
      • Increased HbA1c: hyperbilirubinaemia, alcoholism, large doses of aspirin, chronic opiate use.
      • Variable HbA1c: haemoglobinopathies.
      • Decreased HbA1c: hypertriglyceridaemia.

SETTING GOALS FOR A1C LEVELS

The target A1c level for people with diabetes is usually less than 7%. The higher the hemoglobin A1c, the higher your risk of having complications related to diabetes.

A combination of diet, exercise, and medication can bring your levels down.

People with diabetes should have an A1c test every 3 months to make sure their blood sugar is in their target range. If your diabetes is under good control, you may be able to wait longer between the blood tests. But experts recommend checking at least two times a year.

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